Benzimidazole nucleating agents

ABSTRACT

Direct positive photographs are developed in the presence of nucleating amounts of certain benzimidazoles of defined structure. These nucleating agents can be present in the photographic element itself, in the developing solution employed or in a separate bath.

United States Patent 91 Willis et al.

[ BENZIMIDAZQLE NUCLEATING AGENTS [75] Inventors: Roland George Willis; William Robert Schleigh, both of Rochester, NY.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

22 Filed: Apr. 2, 1973 21 Appl. No.: 347,291

[52] US. Cl. 96/64, 96/76 R, 96/66 R, 96/l07;l08 [51] Int. Cl. G036 1/48, G03c 5/24, G03c 5/30, G030 1/28 [58] Field of Search 96/64, 108, 67, 107, 66 R,

[ 'Nov. 26, R974 [56] References Cited UNITED STATES PATENTS 2,497,917 2/1950 Stauffer 96/64 3,734,738 5/1973 Kurtz et al. 96/107 Primary ExaminerDavid Klein Assistant Examiner-Won H. Louie, Jr. Attorney, Agent, or Firm-C. 0. Thomas ABSTRACT Direct positive photographs are developed in the presence of nucleating amounts of certain benzimidazoles of defined structure. These nucleating agents can be present in the photographic element itself, in the developing solution employed or in a separate bath.

41 Claims, No Drawings BENZHMEAZOLE NUCLEATING AGENTS BACKGROUND OF THE INVENTION 1. Field of the Invention In one aspect, the present invention comprises an improved process for developing direct-positive photographs wherein the improvement comprises carrying out the development in the presence of a nucleating The present invention relates to photography and 5 amount of a benzimidazole of the structure:

more particularly to novel nucleating agents and directpositive photographic emulsions.

2. Description of the Prior Art Certain photographic silver halide emulsions are used to produce positive photographic images without a photographic negative.

Generally, these emulsions are termed direct-positive or reversal emulsions and, on exposure, they tend to form latent images predominantly inside the silver halide grains. The production of direct-positive photographic images is secured by selectively fogging the unexposed regions of a direct-positive photographic layer and developing a conventional photographic silver image corresponding to the unexposed, fogged regions. The fogging agent can be included in a fogging bath with which the imagewise exposed reversal emulsion is treated prior to image development. Alternatively, the fogging agent can be incorporated directly into the developer solution or it can be included in the reversal emulsion prior to coating a photographic layerv Ives, in U.S. Pat. Nos. 2,563,785 and 2,588,982 describes the use of hydrazine compounds in directpositive emulsions of the internal-image type.

Lincoln and Heseltine in U.S. Pat. No. 3,615,615 disclose a variety of aldehyde derivatives of N-acylalkyl heterocyclammonium salts as useful fogging agents in direct-positive, internal-image emulsions.

Belgian patent 774,437 discloses a number of N- substituted heterocyclammonium quaternary salts, in cluding formyl benzothiazolium salts, as nucleating agents for direct-positive, internal-image emulsions.

Staufier in U.S. Pat. No. 2,497,917 describes developing solutions for direct-positive, internal-image emulsions containing ring compounds. These are heterocyclic nitrogen-containing ring compounds having 5 or 6 atoms in the heterocyclic ring and are so constituted as to increase the maximum density of the positive image obtained in developing solutions capable of producing aerial fog. Typical compounds include benzotriazole, methyl benzotriazole, 5-nitroindazole and 6-nitrobenzimidazole British 1,195,838 relates to the use of processing liquids comprising carbazic acid and/or bicarbamic acid and/or at least one water-soluble salt thereof as a fogging compound (or compounds) for partially or wholly replacing an overall exposure step in the production of photographic reversal or direct positive images.

British 1,195,837 relates to a method for the production of direct-positive images by developing in the presence of hydrazine, iodide ions and/or bromide ions.

German 2,015,070 pertains to photographic material for both negative and positive images. The internally ripened grains are fogged.

SUMMARY OF THE INVENTION The present invention relates to the use of certain benzimidazoles as nucleating agents in the treatment of internal-image emulsions after exposure, whereby a developable image is produced on the surface of the grains of the emulsion, which image, when developed, has a density inversely proportional to the degree of the initial exposure.

R R R 6 R I or the structure:

e I I e R N N 5 R N O wherein R R R 40 and R are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, substituted benzyl, substituted phenyl, acetyl, substituted acetyl, amino and alkylamino;

R R R R R R R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, substituted benzyl, substituted phenyl, halogen and ester;

R-, and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, substituted benzyl, substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6- membered cycloalkyl ring; at least one of the groups R and R R and R R and R R, and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

In a preferred embodiment, at least two of R R R R R and R are hydrogen.

In one embodiment of this invention, the benzimidazole nucleating agent is present in at least one layer of the photographic element being developed, said layer being in water-permeable association with the silver halide emulsion of the photographic element.

In another embodiment of this invention, the benzimidazole nucleating agent is present in the developer.

Accordingly, the present invention further comprises (1) a photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising a nucleating amount of a benzimidazole and (2) a photographic developer composition containing a nucleating amount of a benzimidazole; said benzimidazole being of the structure:

or the structure:

N I L 3 R l R 2 7 wherein R R R, and R are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, substituted benzyl, substituted phenyl, acetyl, substituted acetyl, amino and alkylamino;

R R R R R R R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, substituted amino, benzyl, phenyl, substituted benzyl, substituted phenyl, halogen and ester, R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, substituted benzyl, substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6-membered cycloalkyl ring; at least one of the groups R and R R and R R and R R and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring. In preferred embodiments, at least two of R R R R R and R are hydrogen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As stated above, the benzimidazole nucleating agents employed in the practice of this invention are of the structure:

R6 iq R5 5 u i 8 or the structure:

R r 6 I 6 R I I N R t R l l 'U- In these structural formulae, R R R and R can be the same or different and can be hydrogen; alkyl, for

example analkyl group having from 1 to 12 carbon atoms and, preferably,

a lower alkyl group such as one having from 1 to 4 carbon atoms, e.g. methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec.-butyl and tert.-butyl; benzyl, substituted benzyl, e.g., halogen, substituted benzyl, alkyl, especially lower alkyl, substituted benzyl and the like; phenyl; substituted phenyl, e.g. halogen substituted phenyl, alkyl, especially lower alkyl, substituted phenyl, alkoxy, especially lower alkoxy, substituted phenyl and the like; acetyl; substituted acetyl, e.g. halogen substituted acetyl, phenyl substituted acetyl, substituted phenyl substituted acetyl, and the like; amino, including primary, secondary and tertiary amino, particularly alkylamino, which term is intended to include both monoalkylamino and dialkylamino, wherein the alkyl group or groups can have from I to 12 carbon atoms, but preferably are lower alkyl groups of from 1 to 4 carbon atoms.

R R R R R R R and R, can be the same or different and can be hydrogen; alkyl, as described above for R etc.; alkoxy, for example, an alkoxy group having from 1 to 12 carbon atoms and, preferably a lower alkoxy group such as one having from I to 4 carbon atoms, e. g., methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec.-butoxy and tert.-butoxy; nitro; cyano; nitrile amino, i.e. N E C-NH-; amino, including primary, secondary and tertiary amino; substituted amino, including monoalkyl, dialkyl, monoaryl and diaryl substituted amino wherein alkyl can be as described for R etc. and aryl, which term is intended to include substituted aryl, is phenyl, tolyl, xylyl, chlorophenyl, bromophenyl and the like; benzyl, phenyl, substituted benzyl and substituted phenyl as described above for R etc.; halogen, i.e., chloro, fluoro, bromo or iodo; and ester, i.e.,

wherein n is 0 or 1, R is alkyl, preferably lower alkyl or from 1 to 4 carbon atoms and R is also alkyl, preferably having from 1 to 8 carbon atoms and, more preferably, lower alkyl of from I to 4 carbon atoms.

R, and R can be hydrogemalkyl, benzyl, phenyl, substituted benzyl, substituted phenyl, amino, alkoxy, cyano, halogen or ester, all as described above or can be taken together to represent the carbon atoms necessary to complete a 5- or 6-membered cycloalkyl ring which can, if desired, be substituted, for example, lower alkyl substituted, e.g., cyclopentyl, cyclohexyl, methylcyclohexyl, ethylcyclohexyl and the like.

Further, at least one of the groups R, and R R and R R and R or R and R, can be taken together to represent the atoms necessary to complete at least one heterocyclic ring. Preferably, such ring or rings will have 5 or 6 members.

In preferred embodiments, at least two of R R R R R andR are hydrogen.

As exemplary of those compounds useful in the practice of this invention can be listed:

ooo

Spiro[ benzimidazoline-2,l '-cyclohexane] 5-Chloro-l ,3-dim ethyl-2-p henyl-l ,2- dihydrobenzimidazole pi, 7 CH 1 ,3,5-Trimethyl-2-(4-methoxyphenyl l ,2- dihydrobenzimidazole dihydrobenzimidazole 3 N H l fi I 3 CH3 S-Chloro-l ,3-dimethyl-2-( 4 '-methoxyphenyl l ,2- dihydrobenzimidazole I 3 N H cs C;

1,3bimeth i -ll hlom hen l 1,2-

dihydrobenzimidazole 65 The above-described benzrmldazoles are extremely advantageous as incorporated nucleating agents or fogging agents in silver halide reversal or direct-positive emulsions utilized in photographic elements designed for reversal processing to prepare direct-positive photographic images without an intermediate developed negative image. Typical of such direct-positive emulsions are those that form latent images predominantly inside the silver halide grains.

The photographic emulsions generally used in reversal processes are gelatino-silver halide emulsions such as silver bromide, silver bromoiodide, silver chloride, silver chloroiodide, silver chlorobromoiodide or silver chlorobromide emulsions. They need not contain sensitizing dyes although certain of such dyes can be added to reversal emulsions to widen spectral sensitization. Advantageous sensitizing dyes would include those described in US. Pat. No. 2,497,876, especially between column 2, line l5 and column 4, line 20. Internal latent image-forming emulsions are typically undigested or if digested, the digestion is carried out without the use of surface chemical sensitizers. An emulsion of this type, known as Burtons emulsion, is described in Wall Photographic Emulsions, 1927, pp. 52 and 53. Other types of suitable reversal emulsions are the internal latent image emulsions described in Davey and Knott, US. Pat. No. 2,592,250 or those described in Belgian Patent 780,538, issued Mar. 31, 1972.

An internal latent image-forming emulsion can be prepared by first forming in one or more stages silver salt grains consisting at least partly of a silver salt which is more soluble in water than silver bromide, subsequently converting at least part of the grains to silver bromide or silver bromoiodide, ripening, preferably in the absence of ammonia, and then either washing out some of the soluble salts or washing out the whole of the soluble salts, followed by the addition of soluble salts such as soluble chloride, bromide or iodide to prepare a composite silver chlorobromide, bromoiodide or chlorobromoiodide reversal emulsion. Suitable silver chlorobromide internal image emulsions also can be prepared by simultaneously adding an aqueous solution of silver nitrate and an aqueous solution containing potassium chloride and potassium bromide to an agitated aqueous gelatin solution as described in Example 4 of Luckey et al., US. Pat. No. 2,996,382.

An intemal latent image type of silver halide emulsion can be defined as one which, when a test portion p-hydroxyphenylglycine I 10 grams sodium carbonate (crystals) 100 grams water to 1 liter) exhibits a maximum density not greater than l/5 the maximum density obtained when the same emulsion is equally exposed and developed for 3 minutes at 20C in an intemal type developer (one which develops an image inside the grains of an intemal latent image emulsion," which developer type is exemplified by one having the formula:

water to Preferably the maximum density obtained with the surface developer is not greater than H 10 the maximum density obtained when the same emulsion is developed in the intemal type developer. Stated conversely, an internal latent image emulsion, when developed in an internal type developer exhibits a maximum density at least and preferably at least times the maximum density obtained when the emulsion is exposed in the same way and developed in a surface developer.

The subject benzimidazoles that operate advantageously as nucleating agents or fogging agents in internal latent image-forming (reversal) emulsions are conveniently added to a silver halide reversal emulsion, such as, for example, those described in US. Pat. Nos. 2,566,180 or 2,592,250 in amounts designed to produce adequate fog in the form of minute surface development sites which foster the production of directpositive images upon development.

Generally, the fogging agents can be incorporated in at least one layer of the photographic element in waterpermeable association with the silver halide emulsion or they can be contacted with the emulsion before or during development such as by a pre-bath or incorporating the fogging agent in the developer composition; however, the fogging agents are preferably located in at least one layer of the element and in a highly preferred embodiment they are located in the silver halide emulsion layer. Concentrations of from about 75 to about 1,500 mg. of the subject fogging agents per mole of silver in the silver halide emulsion are useful, with from about 90 to about 1,200 mg. of said compounds or agents per mole of silver beingpreferred. It is most preferred to employ from about 90 to about 150 mg. of nucleating agent per mole of silver. These ratios are according to conventional practice, however, and with either particular reversal emulsions, fogging compounds of varying chemical activity, or varying processing conditions, more widely varying fogging agent concentrations can be advantageously used.

The silver halide emulsions employed in the practice of this invention are developed in a silver halide surface developer in the presence of the fogging agents of this invention to provide good positive images. The fogging agents can be incorporated in at least one layer of the silver halide element, which layer is in water-permeable association with the silver halide emulsion, or they can be contacted with said silver halide emulsion by a separate bath or simultaneously with the surface developer composition by incorporating them into the developer composition. Generally, the fogging agents of this invention provide nucleation or fog specks which initiate development of the silver halide in the unexposed areas before initiating substantial development in the exposed areas of an intemal-image emulsion in a surface developer.

Silver halide emulsions into which the benzimidazole nucleating agents of this invention are advantageously incorporated typically. contain other chemical addenda such as, for example, carrier vehicles, spectral sensitizing dyes, coating aids, brighteners, hardeners, developing agents and the like. Desirable carrier vehicles include any of the hydrophilic, water-permeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers and the like, alone or in combination and admixture. The

binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Certain of such compounds are disclosed, for example, in U.S Pat. Nos. 3,142,468 of Nottorf issued July 28, 1964; 3,193,386 of White issued July 6, 1965; 3,062,672 of Houck et al. issued Nov. 6, 1962; and 3,220,844 of Houck et al. issued Nov. 30, 1965; and include the water-insoluble polymers and latex copolymers of alkyl acrylates and methacrylates, acrylic acid sulfoalkyl acrylates or methacrylates and the like.

Spectral sensitizing dyes useful in sensitizing the silver halide emulsions employed in this invention are described in, for example, US. Pat. No. 2,562,632 of Brooker and White issued Oct. 24, 1950 and US. Pat. No. 2,503,776 of Sprague issued Apr. 1 l, 1950. Spectral sensitizers which can be used are the cyanines, merocyanines, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styryls and hemicyanines.

The photographic silver halide emulsions or coatings employed herein can also contain non-ionic, anionic and/or amphoteric coating aids. Some useful coating aids include, for example, saponin, alkyl substituted aryloxyalkylene ethyl sulfonates of the type described in US. Pat. No. 2,600,831 issued June 17, 1952, maleopimarates of the type described in US. Pat. No. 2,823,123, issued Feb. 11, 1958, taurine derivatives of the type described in US. Pat. No. 2,739,891 issued on Mar. 27, 1956, and alkyl aminopropionates of the type described in US. Pat. No. 3,133,816 issued May 19, 1964. Typical of still other good coating aids and surfactants which can be employed in the emulsions of this invention include the alkylphenoxy poly(hydroxyalkylene oxides) such as alkylphenoxy poly(glycidols) having from about 5 to about 12 glycidol units, for example, such as those disclosed in British Patent 1,022,878 issued Mar. 16, 1966.

Advantageous brighteners typically include compounds containing at least one heterocyclic five or six membered ring such as derivatives of stilbene, stilbenetriazole, triazine stilbene, coumarin, triazinylamino coumarin, oxazole, benzidene, benzimidazole, benzothiazole, benzoxazole, pyrazoline, naphthalic acid imide, etc. Exemplary brighteners include such compounds as those described in US. Pat. No. 2,933,390 and US. Pat. No. 3,406,070.

As well as including the above-mentioned addenda, the silver halide emulsions employed in this invention can be hardened with any suitable hardener or combination such as, e.g., formaldehyde, mucochloric acid, glutaraldehyde, maleic dialdehyde, aldehyde hardeners, aziridine hardeners, hardeners which are derivatives of dioxane, vinyl sulfones, oxypolysaccharides such as oxystarch, oxy plant gums, inorganic hardeners such as chromium salts, and the like. Developing agents of the types suitable for inclusion in a silver halide emulsion are described hereinbelow.

To prepare direct-positive photographic elements that can be reversal processed, an internal latent image-forming silver halide emulsion such as described hereinabove, is coated onto a typical photographic support material and dried. Advantageous support materials include conventional photographic film base materials like cellulose esters such as cellulose acetate, cellulose triacetate, cellulose acetate butyrate, etc., polyolefins like polyethylene and polypropylene, polycarbonates, polyesters such as poly(ethylene terephthalate) as well as metals such as zinc and aluminum and paper including polyethylene and polypropylene coated papers. Other support materials that are suitably used herein are known in the art.

The nucleating agents of the invention can be used in reversal color as well as black-and-white silver halide emulsions. The preparation of color reversal photographic elements is conveniently accomplished by employing cyan, magenta and yellow color-forming couplers contiguous to silver halide emulsions capable of recording light substantially complementary in color to the color of dye produced with the respective couplers on color development as described in U.S. Pat. No. 3,227,550 and 3,227,552. Spectral sensitizing dyes can be used to sensitize the silver halide in the usual manner. In a multilayer element, the red-recording emulsion layer can contain a coupler such as -(p amylphenoxy benzene sulfonamino)-1-naphthol, the green-recording emulsion layer, a coupler like 2-cyanoacetyl-5-(p-sec. amylbenzoylamino) coumarone and the blue-recording emulsion layer, a coupler such as N-amyl-p-benzoylacetamino benzene sulfonate. Additional couplers are well known in the art. If desired, the color couplers can be incorporated into the developer solution, as described in Mannes et al., U.S. Pat. No. 2,252,718 and Glass et al., U.S. Pat. No. 2,507,154, such an arrangement necessitating multiple exposures and color developing steps.

After an imagewise exposure, the direct-positive photographic elements containing the subject nucleating agents are immersed in a conventional surface developer solution having relatively low solvent action on silver halide whereupon a positive photographic image is formed. Such surface developers can advantageously contain image-enhancing compounds which increase maximum image density and lower miminum image density such as the benzotriazoles described in Stauffer, U.S. Pat. No. 2,497,917.

If color images are to be prepared, the developer solution typically contains a p-phenylenediamine color developing agent such as a 4amino-N-dialkylaniline like those described in Mees, The Theory of the Photographic Process, 3rd Ed. (1966) pp. 294295. With a color developer, one or more colored dye images are produced depending upon the construction of the particular photographic element. In polychromatic color elements, cyan, magenta and yellow dye images are typically produced in the red sensitive, green sensitive and blue sensitive layers, respectively. Remaining silver is first converted to a soluble silver salt and removed in the usual way by treatment with a fixing agent such as sodium thiosulfate. I

The following examples are included for a further understanding of the invention:

EXAMPLE 1 Spiro[benzimidazoline-2,1'-cyclohexane] This compound is prepared according to the procedure of R. Garner, G. V. Garner, and 1-1. Suschitzky, .1 Chem. Soc. (C), 825 (1970).

A mixture of o-phenylenediamine (10.80 g, 0.1 mole) and cyclohexanone (9.82 g, 0.1 mole) in tetrahydrothiophene-l,l-dioxide (30 ml) is heated 90 minutes on a steam bath. The hot mixture is poured into water. The solid that separates is collected, washed first with water, then with a small volume of ethyl alcohol, and finally with ligroin (b.p. 35-55C). The

washed material is air-dried to yield a yellow solid, 10.52 g, mp. 135C (dec.). Recrystallization from ethyl alcohol gives 5.10 g ofyellow needles (27 percent yield) which decompose at 144C.

EXAMPLE 2 Spiro[ S-nitrobenzimidazoline-Z,1 -cyclohexane] Example 1 is repeated except that 4-nitro-ophenylenediamine is substituted on an equimolar basis for the o-phenylenediamine employed therein. A product having a melting point in the range 160-164C is obtained in 57 percent yield.

EXAMPLE 3 Spiro[ 5-methoxybenzimidazoline-2,l '-cyclohexane] Example 1 is repeated except that 4-methoxy-ophenylenediamine is substituted on an equimolar basis for the o-phenylenedia'mine employed therein. A product having a melting point in the range l04-106C is obtained in 28 percent yield.

EXAMPLE 4 Spiro[ benzimidazoline-2,l '-(4-methylcyclohexane)] Example 1 is repeated except that 4-methylcyclohexanone is substituted on an equimolar basis-for the cyclohexanone employed therein. A product having a melting point in the range 108-1 1 1C is obtained in 60 percent yield.

EXAMPLE 5 1 ,3-Bistrifluoroacetyl-2,3-dihydrobenzimidazole A suspension of PtO (1.0 g) in trifiuoroacetic anhydride (g) is shaken under hydrogen for 5 minutes, then cooled. The reaction vessel is flushed with nitrogen, then benzimidazole (2.36 g, 0.02 mole) is added while the vessel is cooled in an ice bath. The resulting solution is shaken under hydrogen until uptake is complete, then it is filtered and the filtrate concentrated. The residue is recrystallized from ethyl alcohol providing colorless crystals having a melting point of 132C in 66 percent yield.

EXAMPLE 6 S-Methoxy- 1 ,3-bistrifluoroacetyl 2,3- dihydrobenzimidazole Example 5 is repeated except that 5- methoxybenzimidazole is substituted on an equimolar basis for the benzimidazole employed therein. A product having a melting point in the range 104-106C is obtained in 33 percent yield.

EXAMPLE 7 5 ,6-Dimethy1-1 ,3-bistrifluoroacetyl-2,3- dihydrobenzimidazole Example 5 is repeated except that 5,6- dimethylbenzimidazole is substituted on an equimolar basis for the benzimidazole employed therein. A product having a melting point in the range 118121C is obtained in 57 percent yield.

EXAMPLE 8 A 16 mm by 12 inch sample of a photographic element containing an intemal-image silver halide emulsion of the type described in Belgian Patent 780,538 issued Mar. 31, 1972 was exposed (0-6 step tablet, 3,000K, 750W) for 1 second and immersed in a 1-liter bath containing 100 mg of the compound of Example l at a pH of 12.9 at 68F (20C) for 1 minute, washed 'in a 3 percent aqueous acetic acid solution for 2 minutes, in distilled water for.5 minutes and developed in the following surface developer for 5 minutes:

. 5 Table I. I L-ascorbic acid I 10 g. (bkmeghyl-p-aminophenol 2.5 g. EXAMPLES 5!] ate i B mmbmm 4H2) g: The procedure of Example 9 was repeated with each Water to make 1 liter of the compounds of Examples 2 through 7. The results obtained are also shown in Table I. In each instance, a All solutions were deaerated before use and nitrogen Positive m g was obtflined, and h CflmmahO IS burst agitation was employed throughout the process. reflected by a comparison of the silver formed in the The strip was bathed for one minutein 3 percent acetic nexp sed and exposed areas Of the test samples.

TABLE 1 Silver formed (Egg/fiz Exposed Unexposed Compound of Structure (LogE=l 70) (LogE=-O.70) Example No. R' R' General formula H E RI R' H 3 CH 0 H 5 3 I H 3 7 General formula F 06:0

3 H R! l K R' 6 01-1 0 H 12 27 7 CH CH 5 21;

ample 1. The treated sample was bathed in 3 percent acetic acid for one minute, fixed in Kodak Fixing Bath F5 for 10 minutes, water washed for 10 minutes and dried. The photographic results obtained are shown in it-Development timeof 3 min all others 1 min.

acid and 10 minutes in Kodak Fixing Bath F-S (see Handbook of Chemistry and Physics, Forty-First Edition, pp. 3,3153,316), then washed with water for 10 minutes and dried giving a positive image of developed silver. Omission of the pretreatment with the solution containing the compound of Example 1 gave no image.

EXAMPLE 9 EXAMPLE l6 4-Benzyl-2,3 ,3a,4-tetrahydrol H-pyrrolo-[ 1,2- albenzimidazole ori 4 A solution of 7.69 grns. of N-(o-nitrophenyl) pyrrolidine in 75 ml. of ethanol containing 1 gm. of percent palladium on charcoal was shaken under hydrogen until the uptake ceased. The solution was filtered and the filtrate was treated first with 0.04 mole of benzaldehyde and then with a few drops of concentrated HCl. The mixture was stirred overnight under a nitrogen atmosphere and then was concentrated. The residue was distilled in vacuo to yield 5.34 grams of a pale yellow oil having a boiling point of 153C at 0.1 mm Hg. The boiling point of this compound was reported by Grantham et al. in J. Chem. Soc. (C), 1438 (1969) to be 164C at 0.6 mm Hg.

EXAMPLE l7 Benzimidazoline-Z-spiro-l '-cyclohexane-4'-spiro-2 benzimidazoline H H N N U N XXNID This compound was prepared according to the procedure of Example 1 using 0.1 mole of 0- phenylenediarnine and 0.05 mole of cyclohexane-l,4-

dione. Water was the solvent employed. The product was obtained in 90 percent yield and had a melting point of 230233C (dec.).

EXAMPLE l8 1 ,3-Dimethyl-2-(4-methoxyphenyl)-1,2- dihydrobenzimidazole EXAMPLES 19-21 Samples of the exposed photographic element identified in Example 8 were treated according to the procedure of Example 8 except that the nucleating agents were the compounds of Examples l6, l7 and 18, re-- spectively. In each case, well-defined positive images similar to those of Examples 8-15 were obtained.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be .understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. In a process for developing internal latent image silver halide emulsions to produce direct positive photographs, the improvement which comprises carrying out the development with a surface silver halide developer in contact with a nucleating amount of a benzimidazole of the structure:

R R R- g 6 1 5 u- N R8 3 2 or the structure:

' l R N N R R 4 1? R 1 I I R R R 3 V wherein R R R and R' are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkoxy or alkyl substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

R3, R4, R5, R6, RI3, R4, R s and RIG I are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino,

amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl oralkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a5- or 6-membered cycloalkyl ring;

at least one of the group R and R R and R R and R R and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

2. The process of claim 1 wherein the benzimidazole nucleating agent is present in at least one layer of the photographic element being developed.

3. The process of claim 1 wherein the banzimidazole nucleating agent is present in the developer employed to develop the direct positive photographs.

4. The process of claim 1 wherein at least two of R R R R R and R are hydrogen.

5. In a process for developing internal latent image silver halide emulsions to produce direct positive photographs, the improvement which comprises carrying out the development with a surface silver halide developer in the presence of from about to about 1,500 mg. per mole of silver in the silver halide emulsion of a benzimidazole of the structure:

6 fl R N R u N R8 wherein R, and R are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkoxy or alkyl substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

R R,,, R and R,, are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkylv substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6-membered cycloalkyl ring;

at lease one of the groups R, and R R and R,,, R,

and R can be taken together 'to represent the atoms necessary to complete at least one heterocyclic ring.

6. In a process for developing internal latent image silver halide emulsions to produce direct positive photographs, the improvement which comprises carrying out the development with a surface silver halide developer in the presence of a nucleating amount of a benzimidazole of the structure:

N N R 5 4 "5 l t l l R R R R wherein R,, R R', and R, are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

R R,,, R R,,, R,,, R',,, R, and R, are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino,amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

at least one of the groups R, and R,, R, and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

7. The process of claim 5 wherein the benzimidazole is of the structure:

wherein R is hydrogen, nitro or alkoxy and R,, is hydrogen or lower alkyl.

8. The process of claim 7 wherein the benzimidazole is spiro [benzimidazoline-ZJ-cyclohexane 9. The process of claim 7 wherein the benzimidazole is spiro [S-nitrobenzimidazoline 2,l-cyclohexane].

10. The process of claim 7 wherein the benzimidazole is spiro [5-methoxybenzimidazoline-2,1'- cyclohexane]. I

11. The process of claim 7,wherein the benzimidazole is spiro [benziinidazoline-2,l 4'- methylcyclohexane )1.

12. The process of claim 5 wherein the benzimidazole is of the structure:

R R5 H m,

wherein R, and R are halogen orphenyl substituted acetyl and R,, and R are independently selected from the group consisting of hydrogen, alkyl and alkoxy.

13. The process of claim 12 wherein the benzimidazole is l ,3-bistrifluoroacetyl-2,3- dihydrobenzimidazole.

14. The process of claim 12 wherein the benzimidazole is S-methoxyl ,3-bistrifluoroacetyl-2,3- dihydrobenzimidazole.

15. The process of claim 12 wherein the benzimidazole is 5,6-dimethyl-l,3-bistrifluoroacetyl 2,3- dihydrobenzimidazole.

16. A photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising a nucleating amount of benzimidazole of the structure:

' R R R 6 l l R u N R I or the structure: v

l R N C N R H RLl- 7 Fl R R R 1 wherein R,, R R, and R, are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkoxy or alkyl substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

R R R,,, R,,, R',,, R,,, R' and R, are independently selected from the group consisting of hydrogemalkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substitutedbenzyl,

' halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substi- 17. The element of claim 16 wherein at least two of R,, R R R R and R arehydrogen.

18. A photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising from about 75 to about 1,500 mg per mole of silver in the silver halide emulsion of a benzimidazole of the structure:

wherein R, and R are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, acetyl, halogen'or phenyl substituted acetyl, and amino;

R R R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6-membered cycloalkyl ring;

at least one of the groups R and R R and R R and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

19. A photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising a nucleating amount of benzimidazole of the structure:

R R R l and R' are independently selected from the group consisting of hydrogen, alkyl, benzyl,

phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

5 R R R R R' R R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

at least one of the groups R and R R, and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring. 20. The element of claim 18 wherein the benzimidazole is of the structure:

wherein R is hydrogen, nitro or alkoxy and R is hydrogen or lower alkyl.

21. The element of claim 20 wherein the benzimidazole is spiro [benzimidazoline-2,l -cyclohexane].

22. The element of claim 20 wherein the benzimidazole is spiro [5-nitrobenzimidazoline-2, l cyclohexane].

23. The element of claim 20 wherein the benzimidazole is spiro [5-methoxybenzimidazoline-2,l cyclohexane].

24. The element of claim 20 wherein the benzimidazole is spiro benzimidazoline-2,l -(4'- methylcyclohexane)].

25. The element of claim 18 wherein the benzimidazole is of the structure:

1 l R N H wherein R R R and R' are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, acetyl, halogen or alkyl substituted acetyl, and amino;

R R R R R R,, R' and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6-membered mg per mole of silver in the silver halide emulsion to be developed of benzimidazole of the structure:

R and R are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, phenyl or halogen substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, acetyl, halogen or alkyl substituted acetyl, and amino;

R R R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

R and R are selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, amino, alkoxy, cyano, halogen and ester, or are taken together to represent the carbon atoms necessary to complete a 5- or 6-membered cycloalkyl ring;

at least one of the groups R and R R and R R and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

32. A photographic silver halide surface developer composition containing a nucleating amount of a benzimidazole of the structure:

i 22 6 51 ii e; R N N R5 R gimp R R R R wherein R R R and R' are independently selected from the group consisting of hydrogen, alkyl, benzyl, phenyl, halogen or alkyl substituted benzyl, substituted phenyl, acetyl, halogen or phenyl substituted acetyl, and amino;

R R R R R' R' R and R are independently selected from the group consisting of hydrogen, alkyl, alkoxy, nitro, cyano, nitrile amino, amino, benzyl, phenyl, halogen or alkyl substituted benzyl, halogen, alkyl or alkoxy substituted phenyl, halogen and ester;

at least one of the groups R and R R l and R can be taken together to represent the atoms necessary to complete at least one heterocyclic ring.

33. The developer of claim 31 wherein the benzimidazole is of the structure:

37. The developer of claim 33 wherein the benzimidazole is spiro methylcyclohexane] 38. The developer of claim 31 wherein the benzimidazole is of the structure:

[benzimidazoline-2,l -(4- R N H wherein R and R are substituted acetyl and R and R are independently selected from the group consisting of hydrogen, alkyl and alkoxy.

39. The developer of claim 38 wherein the benzimidazole is l ,3-bistrifluoroacetyl-2,3- dihydrobenzimidazole.

40. The developer of claim 38 wherein the benzimidazole is S-methoxy-l ,3-bistrifluoroacetyl-2,3- dihydrobenzimidazole.

41. The developer of claim 38 wherein the benzimidazole is 5 ,6-dimethyl-l ,3-bistrifluoroacetyl-2,3-

dihydrobenzimidazole. 

1. IN A PROCESS FOR DEVELOPING INTERNAL LATENT IMAGE SILVER HALIDE EMULSIONS TO PRODUCE DIRECT POSITIVE PHOTOGRAPHS, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE DEVELOPMENT WITH A SURFACE SILVER HALIDE DEVELOPER IN CONTACT WITH A NUCLEATING AMOUNT OF A BENZIMIDAZOLE OF THE STRUCTURE:
 2. The process of claim 1 wherein the benzimidazole nucleating agent is present in at least one layer of the photographic element being developed.
 3. The process of claim 1 wherein the banzimidazole nucleating agent is present in the developer employed to develop the direct positive photographs.
 4. The process of claim 1 wherein at least two of R1, R2, R3, R4, R5 and R6 are hydrogen.
 5. In a process for developing internal latent image silver halide emulsions to produce direct positive photographs, the improvement which comprises carrying out the development with a surface silver halide developer in the presence of from about 75 to about 1,500 mg. per mole of silver in the silver halide emulsion of a benzimidazole of the structure:
 6. In a process for developing internal latent image silver halide emulsions to produce direct positive photographs, the improvement which comprises carrying out the development with a surface silver halide developer in the presence of a nucleating amount of a benzimidazole of the structure:
 7. The process of claim 5 wherein the benzimidazole is of the structure:
 8. The process of claim 7 wherein the benzimidazole is spiro (benzimidazoline-2,1''-cyclohexane ).
 9. The process of claim 7 wherein the benzimidazole is spiro (5-nitrobenzimidazoline 2,1''-cyclohexane).
 10. The process of claim 7 wherein the benzimidazole is spiro (5-methoxybenzimidazoline-2,1''-cyclohexane).
 11. The process of claim 7 wherein the benzimidazole is spiro (benzimidazoline-2,1''-(4''-methylcyclohexane)).
 12. The process of claim 5 wherein the benzimidazole is of the structure:
 13. The process of claim 12 wherein the benzimidazole is 1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 14. The process of claim 12 wherein the benzimidazole is 5-methoxy-1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 15. The process of claim 12 wherein the benzimidazole is 5,6-dimethyl-1,3-bistrifluoroacetyl 2,3-dihydrobenzimidazole.
 16. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT HAVING DEPOSITED THEREON AT LEAST ONE LAYER COMPRISING A SILVER HALIDE INTERNAL-IMAGE PHOTOGRAPHIC EMULSION AND AT LEAST ONE LAYER IN WATER-PERMEABLE ASSOCIATION WITH SAID SILVER HALIDE LAYER COMPRISING A NUCLEATING AMOUNT OF BENZIMIDAZOLE OF THE STRUCTURE:
 17. The element of claim 16 wherein at least two of R1, R2, R3, R4, R5 and R6 are hydrogen.
 18. A photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising from about 75 to about 1,500 mg per mole of silver in the silver halide emulsion of a benzimidazole of the structure:
 19. A photographic element comprising a support having deposited thereon at least one layer comprising a silver halide internal-image photographic emulsion and at least one layer in water-permeable association with said silver halide layer comprising a nucleating amount of benzimidazole of the structure:
 20. The element of claim 18 wherein the benzimidazole is of the structure:
 21. The element of claim 20 wherein the benzimidazole is spiro (benzimidazoline-2,1''-cyclohexane).
 22. The element of claim 20 wherein the benzimidazole is spiro (5-nitrobenzimidazoline-2,1''-cyclohexane).
 23. The element of claim 20 wherein the benzimidazole is spiro (5-methoxybenzimidazoline-2,1''-cyclohexane).
 24. The element of claim 20 wherein the benzimidazole is spiro (benzimidazoline-2,1''-(4''-methylcyclohexane)).
 25. The element of claim 18 wherein the benzimidazole is of the structure:
 26. The element of claim 25 wherein the benzimidazole is 1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 27. The element of claim 25 wherein the benzimidazole is 5-methoxy-1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 28. The element of claim 25 wherein the benzimidazole is 5,6-dimethyl-1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 29. A PHOTOGRAPHIC SILVER HALIDE SURFACE DEVELOPER COMPOSITION CONTAINING A NUCLEATING AMOUNT OF A BENZIMIDAZOLE OF THE STRUCTURE:
 30. The developer of claim 29 wherein at least two of R1, R2, R3, R4, R5 and R6 are hydrogen.
 31. A photographic silver halide surface developer composition containing from about 75 to about 1,500 mg per mole of silver in the silver halide emulsion to be developed of benzimidazole of the structure:
 32. A photographic silver halide surface developer composition containing a nucleating amount of a benzimidazole of the structure:
 33. The developer of claim 31 wherein the benzimidazole is of the structure:
 34. The developer of claim 33 wherein the benzimidazole is spiro (benzimidazoline-2,1''-cyclohexane).
 35. The developer of claim 33 wherein the benzimidazole is spiro (5nitrobenzimidazoline-2,1''-cyclohexane).
 36. The developer of claim 33 wherein the benzimidazole is spiro (5-methoxybenzimidazoline-2,1''-cyclohexane).
 37. The developer of claim 33 wherein the benzimidazole is spiro (benzimidazoline-2,1''-(4''-methylcyclohexane).
 38. The developer of claim 31 wherein the benzimidazole is of the structure:
 39. The developer of claim 38 wherein the benzimidazole is 1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 40. The developer of claim 38 wherein the benzimidazole is 5-methoxy-1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole.
 41. The developer of claim 38 wherein the benzimidazole is 5,6-dimethyl-1,3-bistrifluoroacetyl-2,3-dihydrobenzimidazole. 